This invention relates to a medical instrument and a method for the surface treatment thereof.
Medical appliances, for example, medical instruments such as catheters which are inserted through airway, trachea, alimentary canal, urethra, blood vessels or other celoms or tissues, and medical instruments such as guide wires or stylets which are inserted through catheters are required to have smoothness for assuring the introduction of such medical instruments into a desired region of the body without injuring tissues. Such medical instruments are further required to have lubricity for preventing injury or inflammation of mucous membrane which would be caused when the instruments stay in the tissues.
For this reason, substrates of which such medical instruments are made are, heretofore, made of ordinary low-frictional resistance materials such as fluoroplastics and polyethylene, or coated with a surface layer of fluoroplastics, silicone or the like. In another instance, silicone oil, olive oil, glycerine, xylocain jelly or the like is applied to the substrate surface.
However, these conventional techniques are not satisfactory in effect. For example, in case low-frictional resistance materials such as Teflon (trade mark, manufactured by DuPont), high-density polyethylene, etc. are employed or substrates are coated with a surface coat of such materials, there is the problem that coefficients of friction are not low enough. In case oils are applied, coefficients of dynamic friction are sufficiently low, but there is another problem that oils tends to run off and the effect does not last. In addition, products with oil applied has smeary surfaces and are difficult to store. Therefore, oil application must be done immediately before use, which would make the handling complicated.
U.S. Pat. No. 4,100,309 discloses the use of an interpolymer of polyvinyl pyrrolidone and polyurethane as a coating layer on the outer and inner surfaces of a catheter tube. This coating layer is superior in frictional resistance and its retention to other types of conventional coatings.
This coating layer, however, needs an isocyanate group as a reactive functional group and polyurethane as a substrate or an undercoat on a substrate. Thus, the choice of the substrate and the application of the resultant medical instrument are disadvantageously limited. For example, if such a coating layer is applied to a polyamide resin, it is difficult to directly introduce isocyanate group. Even if polyurethane is used as an undercoat, bonding to the substrate is not good and formation of a durable coating layer is not expected. In addition, polyvinyl pyrrolidone is relatively expensive.
Furthermore, it is considered that polyvinyl pyrrolidone and isocyanate group forms an ion complex. Therefore, the bond is not stable in aqueous solutions for example, humor such as saliva, digestive fluid, blood or the like, or physiological saline and the complex tends to be dissolved in such solution. Thus, lasting effect is not expected. The retention of low frictional resistance is very important for medical tube guides which are used under severe sliding conditions as contemplated in the present invention.
The above-mentioned U.S. Patent includes no disclosure or indication that the coating layer can be applied to catheter guides as in the present invention, thereby remarkably improving the sliding resistance thereof and solving the problems of manipulation and safety.
Japanese Patent Application Kokai No. 53-106778 discloses a method for providing a fibrinolytic activity to the surface of polyurethane resins wherein fibrinolysis activators are affixed to the surface of polyurethane resins. According to this disclosure, a polymer containing maleic anhydride units is used as an intermediate bonding layer for affixing the fibrinolysis activator on the polyurethane surface so that the layer of fibrinolysis activator formed as an outer surface may be dissolved to provide anticoagulant properties. There is no disclosure or suggestion of enhancing the lubricity of medical instruments.
Guide wires which are typical of medical instruments have the following problems.
The medical guide wires used in the prior art generally include coiled guide wires formed of stainless steel or piano wires and monofilament-like guide wires formed of plastic materials. In order that the guide wire has a flexible tip and a relatively rigid base, the guide wire is constructed so as to include a core of general metals such as stainless steel and piano wires partially or entirely in the interior thereof.
As typically encountered in indwelling a vasographic catheter at the predetermined vessel site, the guide wire is inserted through a catheter up to its tip opening, the catheter with the guide wire is inserted into the blood vessel through an introduction needle percutaneously, and the catheter was further inserted through the vessel by using the guide wire as a leading and supporting guide.
In order that the catheter tip reaches the destined vessel site, the guide wire tip protrudes a distance of a few centimeters beyond the distal opening of the catheter. The exposed or extended tip portion of the guide wire is advanced through the vessel in contact with the inner wall of the vessel. The tip portion should be sufficiently soft and flexible so that it may easily conform to irregularities on the vessel inner wall and bends at vessel branches to effectively guide the catheter.
In such operation, it is first of all desired that the frictional resistance between the catheter inner surface and the guide wire is low. Relatively high friction between the catheter and the guide wire not only prevents the guide wire from being inserted through the catheter, but the guide wire from being slidingly moved through the catheter, making it difficult to carry out subtle indwelling operation at the destined vessel site. Sometimes the guide wire cannot be withdrawn from the catheter, rendering the catheter lumen unusable despite the completion of indwelling operation.
To avoid such inconvenience, attempts have been made in the prior art to apply low frictional resistance Teflon and silicone oil to the outer surface of guide wires. Application of silicone oil fails to retain lubricity because of immediate loss of silicone coatings. Frequent applications add to frictional resistance, also undesirably creating troubles as mentioned above.
These attempts are still insufficient. There is thus the need for a guide wire having a lower frictional resistance surface which enables more subtle operation in a vessel as well as in the associated catheter and can be easily indwelled at the site where catheters are otherwise difficult to stay.
A second problem is encountered when the guide wire tip preceding the catheter is advanced through the vessel. When the guide wire tip passes a plurality of vessel branches or complicated branches or slender branches suddenly from a thick vessel, the guide wire tip is first abutted against the branch. It must be observed whether the tip is deflected to the right or the left. The guide wire is further advanced when the tip turns on the side of the destined site.
It is thus necessary that the guide wire tip can move along the vessel wall in a sliding manner with a sufficiently low force. Tip portions used in the prior art are made as flexible as possible, but still insufficient. One recent attempt is to form a spherical tip to weaken the impact of the tip against the vessel wall and to locally concentrate a force to the base of the spherical tip to provide ease of bending, thereby facilitating lateral motion of the tip. As the tip is further guided to the second and third branches, the tip experiences increased resistance to the vessel wall. Since the catheter is also advanced in curved form, the guide wire experiences increased friction within the catheter, making the inserting operation less smooth.